Wet spinning of cellulose triesters



United States Patent 3,267,189 WET SPINNHNG 0F CELLUILOSE TRIESTERS Cipriano Cipriani, Morristown, and John W. Soehngen,

Berkeley Heights, N..l., assignors to Celanese Corporation of America, New York, N.Y., a corporation of Delaware N0 Drawing. ()riginal application Sept. 27, 1960, Ser. No. 58,610. Divided and this application Nov. 7, 1962, Ser. No. 236,147

'7 Claims. (Cl. 264-129) This is a continuation-in-part of our application Serial No. 850,531, filed November 3, 1959, now Patent No. 3,109,697, and a division of our application Serial No. 58,610, filed September 27, 1960, now abandoned.

The present invention relates to the wet spinning of organic acid esters of cellulose containing fewer than about 0.29 free hydroxyl groups per anhydroglucose unit of the cellulose molecule, particularly cellulose triacetate.

US. patent application Serial No. 730,021 filed April 21, 1958 now Patent No. 3,057,039, in the name of Jesse L. Riley discloses the wet spinning of a solution of a cellulose triester into a coagulant or spin bath which contains both a non-solvent for the cellulose triester, the spin bath exerting a swelling action on the freshly formed filaments, the filaments being drawn down, i.e. pulled out of the bath at a linear speed of about 1 to 20 and preferably about 5 to times the extrusion speed. Preferably the cellulose triester is cellulose triacetate having an acetyl value of at least about 60% and generally above 61% calculated as combined acetic acid and is employed as a solution of about 18 to 26% concentration by weight in a solvent comprising a halogenated lower alkane which may contain up to about 15% by weight of a lower alkanol, e.g. methylene chloride plus methanol. The spin bath is preferably also made up of the halogenated alkane and alkanol, except that the alkanol proportion is sulficiently high to effect precipitation of the cellulose triacetate. The halogenated alkane concentration may range from about to 65% by weight of the spin bath, its concentration desirably varying inversely with the temperature of the spin bath which may range from about room temperature up to about the boil, e.g. about 15 to C. When the halogenated alkane concentration in the spin bath, C, is approximately related to the spin bath temperature, T, by the equation C=75 ATi5 it has been found that the resulting filaments, under the prevailing spinning conditions, will simultaneously exhibit higher tenacity and elongation than if the spin bath concentration is varied slightly either up or down.

The resulting products exhibit excellent physical properties and can readily be distinguished from other filamentary materials such as dry spun cellulose triacetate, for example.

The individual filaments are generally substantially circular in cross-section, in contrast to the bulbous or potato-shaped cross-section of dry-spun filaments. Also, stress-strain curves for the wet-spun cellulose triacetate filaments show a higher modulus of elasticity and higher resistance to deformation throughout the whole range of strain, as compared with dry-spun cellulose triacetate filaments.

The filaments produced in accordance with the Riley disclosure exhibit tenacities in excess of about 1.8 and usually 2 grams per denier at elongations of at least about 18 and usually 20%, even for filaments whose denier is in the range of 1.5 to 4. The energy of rupture, i.e. the area under the stress-strain curve from Zero stretch to break, is high, above 800 dyne cm. for 1 cm. of a 3 denier filament. These filamentary materials are characterized by radial uniformity. This can be deter mined by treating the filamentary materials with a saponifying agent which deesterifies the surface portions of the filamentary material, forming a cellulose skin which is then removed with a solvent for cellulose. When subjected to this treatment a filamentary material which is non-uniform exhibits different properties as compared with the original material, while a radially uniform material has the same properties as before.

In testing for radial uniformity the surface removal can be effected, for example, by wetting the filaments to be tested in cold Water containing 0.1 gram per liter of Triton X-100 (iso-octyl phenyl ether of polyethylene glycol) then immersing them in 1000 times their weight of a 50 grams per liter solution of sodium hydroxide at C. for from 30 seconds to 3 minutes, and quickly transferring them to cold running water for 5 minutes. The filaments are then soured in acetic acid for 15 minutes, and again rinsed in running water for 15 minutes. After drying in air, the filaments are immersed at room temperature for 3 minutes in a solution made up of equal weights of cupriethylene diamine and water to dissolve the cellulose skin formed by the saponification. The filaments are then rised, soured, rinsed and dried as before.

The foregoing treatments of course reduce the filament denier but the tenacity in grams per denier is not changed. The percent elongation also remains unchanged. X-ray diffraction patterns, microscopic observations and other properties are also the same for the starting material and for specimens from which surface layers of different thickness are removed. The safe-ironing temperature following heat treatment is also the same whether or not the filament is de-surfaced.

Whereas surface removal of dry spun cellulose triacetate effects a marked increase in the rate of dyeing, surface removal of wet-spun cellulose triacetate filamentary material does not similarly affect the dyeing rate. This is demonstrated as follows: Dry spun cellulose triacetate filaments of 3.75 denier when immersed in a dyebath took up 0.18% of their weight of dyestuif after being immersed in the dyebath for 5 minutes and 0.22% of their weight after 15 minutes immersion. If these filaments are first treated as described to remove a surface layer 44 l0 cm. thick, the filaments under identical dyeing conditions will pick up 0.22% by weight of dyestuff in 5 minutes and 0.30% in 15 minutes. This appreciable increase in pick up evidences radial heterogeneity in the filaments.

By way of comparison 2.5 denier wet-spun filaments pick up 0.24% by weight of dyestuff after being immersed 5 minutes in the dyebath previously set forth and 0.34% after 15 minutes. Removal of a surface layer 47x10 cm. thick does not increase the dyeing rate. Actually there is a slight decrease to 0.23% and 0.31% in 5 and 15 minutes, respectively, i.e. approximately the same rate as de-surfaced dry spun cellulose triacetate filaments. This slight decrease in the dyestuff pick up rate of desurfaced wet spun filaments as opposed to wet spun filaments which have not been de-surfaced is due to the fact that the wet spun filaments initially have a slightly pebbled surface which is smoothed out upon desurfacing thereby reducing slightly the surface to volume ratio of the filaments.

In the above tests the dyebath was water containing 50 grams per liter of dispersed Amacel Red 2B (a red cellulose acetate dye), 1 gram per liter of Igepon T-51 (a dispersing agent) and 1 gram per liter of sodium hexametaphosphate; the bath was maintained at 95 C.

The filamentary materials show a relatively high overall birefringence after complete saponification of said materials. The overall birefringence of the saponified material is above about 0.031, typical values being in the range of about 0.034 to 0.037. This overall birefringence is the sum of the birefringences through the fiber and is measured, in conventional manner, by a transmission technique. In the complete saponification method employed for this purpose, the filamentary material is saponified completely by immersion for at least 30 minutes in 100 times its weight of a solution containing, by weight parts of sodium hydroxide, 12 parts of sodium acetate, parts of dimethylsulfoxide and 73 parts of water, at 80 C. Completion of saponification can be checked by wetting the filamentary material with l-N cupriethylene diamine solution; if, as viewed under a microscope, the filamentary material dissolves completely in 30 seconds, saponification is complete; if not complete, the time of immersion in the saponifying liquor can be increased. When it has been determined that saponification is complete, the filamentary material is rinsed with distilled water until the rinse water is neutral. The saponified material is air dried. The treatment does not cause shrinkage or loss of strength. The overall birefringence, as opposed to merely surface birefringence, is determined in customary manner, as with a Berek compensator using polarized light.

Cellulose triacetate filamentary materials produced by wet spinning as described hereinabove exhibit definite rubbery properties at elevated temperatures. This is demonstrated in the following manner: A 125 denier 40 filament yarn is held at constant length (e.g. 10 inches) and heated to a temperature of 220 C. at a just perceptible initial tension (about 0.03 g.). The temperature is then cycled between 217 C. and 223 C. It will be found that the tension on the filament increases as the temperature increases and decreases very perceptibly as the temperature decreases, typical of a rubber. By way of comparison, if the temperature of the filament is cycled between 162 C. and 168 C., the tension will be found to decrease as the temperature increases, typical of a glass.

Like other cellulose triacetate filamentary material, the above-described cellulose triacetate filamentary material may be heat treated to raise the safe ironing temperature of fabrics produced therefrom and to improve the dimensional stability, resistance to creasing, permanence of pleating, and the like. However, the wet-spun filamentary material shows substantially no shrinkage or decrease of tenacity on such heat treatment. In fact, the tenacity may even increase. For example, a filament having an original tenacity of 2.15 grams per denier, when heat treated in air at 210 C. for 5 minutes shrinks less than 1% and has a final tenacity of 2.37 grams per denier.

Such cellulose triacetate filamentary material is also characterized by resistance to creep at elevated temperature. This is demonstrated as follows: One end of a filament is anchored within a horizontal heating tube. 10 inches from the anchored end, the filament is knotted to a glass filament which extends outside the tube and runs over a pulley. A weight is suspended from the protruding end of the glass filament. With various size weights suspended from the glass filament the tube is heated and the displacement of the weight with change in temperature is noted. Cellulose triacetate filaments produced by dry spinning the initial solutions begin to creep at about 168 C. The wet-spun filamentary materials do not creep comparably below about l78-183 C. The rate and amount of creep for dry-spun filaments under a load of 0.033 gram per denier are only reached for the wet-spun filamentary materials at a load equal to or in excess of 0.067 gram per denier.

In producing such filaments they occasionally exhibit a tendency to coalesce or adhere to one another. One way to overcome this tendency and to avoid coalescence is described in U.S. patent application Serial No. 729,980 filed April 21, 1958 in the name of John W. Soehngen and involves the removal of the adherent spin bath from the freshly formed swollen filaments while the filaments are maintained separated and substantially tensionless, as by passage through an air jet provided with hot air. This treatment also serves to introduce a crimp into the filaments with no physical damage such as accompanies mechanical crimping. The crimps in adjacent filaments of the bundle or tow are randomly arranged, out of alignment; the crimp being three-dimensional, either helically or randomly three-dimensional, and not substantially in a single plane. Thus, the tow is much more voluminous or lofty than the conventional tows. When the tow is cut into staple fiber lengths and then processed in the conventional manner to produce staple fiber yarn, much less breakage of filaments and formation of undesirable short filaments or fly takes place. Also, because of the voluminous character of the material, much less mechanical processing is necessary to open or separate the staple fibers before they are formed into yarns.

Typical crimped filaments contain 8 or more, e.g. 8 to 12, fine crimps per inch, the amplitude of the crimp being irregular but generally being on the order of 1 mm. and the percent crimp, based on the straightened length, being above about 4%. Percent crimp is defined as Straightened length-crimped length Straightened length It is an object of the present invention to provide an alternate procedure for avoiding coalescence of the wet spun filaments of cellulose trieste-rs.

It is a further object of the invention to provide a process which permits production of cellulose triester filamentary material of improved physical properties.

Another object is to provide a process for producing cellulose triester filamentary material which can easily be handled in staple fiber form and can be converted into yarn in conventional manner.

Other objects and advantages of the invention will be apparent from the following detailed description and claims, wherein all proportions are by weight unless otherwise specified.

In accordance with one aspect of the invention, the coagulated cellulose triester filamentary material produced by extrusion into a spin bath exerting a swelling action thereon, prior to drying and while still swollen, is immersed in a bath containing a hydrocarbon oil having an aliphatic chain of at least about 14 atoms and having a molecular weight of at least about 200 and preferably about 300 to 1000. 'In addition, the hydrocarbon oil desirably should melt below about 50 C. and preferably below about 40 C. and should boil above about 200 C. and preferably above about 250 C. It should be soluble in cellulose triacetate to the extent of less than about 10% and preferably less than about 5% by Weight, the solubility being measured as follows: a weighed amount of 3 denier filaments of cellulose triacetate are immersed in the compound in liquid form at 50 C. for 5 minutes, the filaments are withdrawn and rinsed in perchlorethylene for 10 minutes to remove surface material. The filaments are now Soxhlet extracted with diethyl ether for 30 minutes and the ether extract is weighed after evaporation. The weight divided by the dry filament weight and multiplied by 100 is the percent solubility. Alternatively, if the weight of the compound is assumed to be the difference between the weight after drying following the perchlorethylene rinse and the initial dry weight, the solubility results will be almost as precise.

The hydrocarbon oils effect a marked improvement in processability, i.e. even staple fibers of very low denier can be carded with ease on a conventional cotton card, they are inexpensive and when the fiber or fabric made therefrom is being prepared for dyeing they can easily be scoured off. Desirably, the hydrocarbon oil is a white mineral oil having an essentially aliphatic base, such as paraffinic or naphthenic base, and having a viscosity of about 30 to 400 seconds as measured at 38 C. (100 F.) in the Saybolt Universal viscosimeter, and preferably a viscosity of about 40 to 100 seconds. Its molecular weight desirably ranges fro-m about 175 to 400 and preferably about 200 to 300. Its initial boiling point generally is in excess of about 200 C. .and preferably in excess of about 250 C. and its vapor pressure is generally less than about 0.1 mm. Hg at 38 C.

The invention will be further described with reference to the preferred hydrocarbon oils. Desirably the hydrocarbon oil is present during the very formation of filaments, as by being present in the spin bath and/ or dope. The presence of hydrocarbon oil in the spin bath, for example, surprisingly improves the spinning stability, i.e. at a given spinning speed there are fewer broken fils or for a given number of fil breaks the maximum permissible spinning speed is higher with hydrocarbon oil in the spin bath. While not wishing to be bound thereby it is believed that the hydrocarbon oil retards the rate of coagulation of the filaments. As any rate, the filaments exhibit higher tenacities and/or elongation than when no hydrocarbon oil is in the spin bath, the tensile factor, i.e. Tenacity /Elongation, often being or more greater than without the hydrocarbon oil. The loop tensile properties are also improved by the presence of the hydrocarbon oil, the product exhibiting increased resistance to abrasion .and flexural fatigue.

Alternatively the hydrocarbon oil may be applied to the filaments in a bath subsequent to the spinning apparatus and the improvement in processability will still be realized. In the event the particular process calls for a wash liquid following filament-formation, the hydrocarbon oil may be added to such wash liquid either dispersed or dissolved therein. In the event a wash liquid is employed even if the hydrocarbon oil is in the spin bath it may be necessary to add hydrocarbon oil to the wash liquid to prevent its complete removal from the filaments, as will occur where the wash liquid is too good a solvent for the hydrocarbon oil.

Where the hydrocarbon oil is included in the spin bath it is generally present in about 0.1 to 3% and preferably 0.5 to 1%, based on the spin bath weight, to exert its beneficial effect to a substantial degree. Lower proportions result in a lesser improvement while higher proportions are less economical and do not especially improve the results achieved. If the mineral oil is added as a dispersion or solution along with other materials, erg. pigments, anti-static agents or the like, the dispersion or solutions is obviously added in amount sufficient to provide the desired percentage of the hydrocarbon oil component.

The exact proportion of hydrocarbon oil in the spin bath will vary with factors such as the feed ratio of spin bath to filamentary material, the denier and residence time of the filamentary material in the spin bath, the degree of extraction of spent spin bath from the filaments as they leave the spin bath, and the like. All factors considered, the concentration of hydrocarbon oil should generally be sufficient to leave about 0.1 to 5% and preferably about 0.5 to 2% of hydrocarbon oil on the filaments based on the dry weigh-t of the filaments.

If the hydrocarbon oil is present in a wash liquid in stead of, or in addition to, the spin bath, the concentration will be such as to leave approximately the same amount of hydrocarbon oil on the filaments.

After leaving the spinning apparatus, and the wash apparatus i-f employed, the wet filaments carrying the hydrocarbon oil can be dried in any desired manner and may be lubricated in conventional manner, although such lubrication is not necessary. Preferably an anti-static agent is applied at this stage so that the agent Is on the outside of the filaments where it exerts its action to the fullest extent, although it may be present in the spin bath, a wash liquid or the like. The filaments can then be cut and carded on conventional cotton carding equipment without difficulty. By contrast, if hydrocarbon oil is omitted from the spin bath and instead is sprayed on along with antistatic agent after dryin in amount suifioient to leave on the filaments the same proportion of hydrocarbon oil, the extrusion is less stable, the physical properties of the product are not as good, there is a moderate amount of coalescence and the product when out into staple can be carded only with difficulty, requiring special card clothing and/or repeated passes through the carding apparatus. The improvement in cardability is most striking when producing fibers of about 2 denier or less since only by the present invention can such low denier fibers be carded in a single pass on the conventional carding equipment equipped with fillet wire clothing.

The hydrocarbon oil is distributed substantially uniformly on the surface of the filaments, as contrasted with the discontinuous film produced by spraying or brushing hydrocarbon oil onto dry filaments. The anti-static agent, when present, floats on the thin hydrocarbon oil layer.

While the invention has been described principally with reference to triesters of cellulose with acetic acid, it can be applied also to esters with formic, propionic, butyric, nitric, and like acids, as well as to esters with mixtures of these acids with one another and/or acetic acid. Throughout this specification and appended claims where reference is made to immersion of the filamentary material this can be effected either by submersion, by pass-age through a cascade wherein the filaments are fully wet out or other procedures wherein the filaments become soaked.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of our invention.

Having described our invention what we desire to secure by Letters Patent is:

1. The process which comprises extruding a solution of a cellulose triester into a coagulant spin bath, withdrawing the resulting swollen wet spun cellulose triester filamentary material from said spin bath, and. immersing said swollen filamentary material in a subsequent bath containing a hydrocarbon oil having an aliphatic chain of at least about 14 atoms and having a molecular weight of at least about 200, a melting point below about 50 C., a boiling point of at least about 200 C. and being less than about 10% soluble in said cellulose triester, and thereafter drying said filamentary material.

2. The process according to claim 1, including the further steps of applying an anti-static agent to said fila mentary material, cutting said filamentary material into staple fibers, and carding said staple fibers on a card equipped with fillet wire clothing.

3. The process according to claim 11, wherein said hydrocarbon oil is also present in said spin bath in an amount ranging from about 0.1 to 3% by weight.

4. The process according to claim 1, wherein said hydrocarbon oil is present in said bath in an amount sulficient to deposit on said filamentary material about 0.1 to 5% of said compound based on the Weight of said filamentary material.

5. The process according to claim 1, wherein said filamentary material on a dry basis is less than about 2. denier per fil.

6. The process which comprises extruding a solution of cellulose triacetate into a coagulant spin bath, withdrawing the resulting swollen wet spun cellulose triacetate filamentary material from said spin bath, and immersing said swollen filamentary material in a subsequent bath containing an aliphatic hydrocarbon oil present in an amount suflicient to deposit on said filamentary material about 0.1 to 5% of its weight of said hydrocarbon oil.

7. The process according to claim 6, including the further steps of applying an anti-static agent to said filamentary material, cutting said filamentary material into staple fibers, and carding sai-d staple fibers on a card equipped with fillet Wire clothing.

References Cited by the Examiner UNITED STATES PATENTS Donaldson et a1. 117144 X Taylor et al. 264200 X 8 Lakatos et al. 117144 Tompkins 2528.9 Kiefer et a1. 131208 Lichtb-la-u i 117144 Wentworth 117-144 Xv Groombridge et a1.

Rulison.

OTHER REFERENCES 10 Textile Chemicals and Auxiliaries, S-peel et aL, published in 1957 by Rheinhold lpp. 114-1 1 6 are relied upon.

ALEXANDER H. BROD'MERKEL, Primwry Examiner.

WILLIAM J. STEPHENSON, MORRIS LIEBMAN,

Examiners.

C. B. HAMBURG, K. W. VERNON, A. L. LEAVITI',

Assistant Examiners. 

1. THE PROCESS WHICH COMPRISES EXTRUDING A SOLUTION OF A CELLULOSE TRIESTER INTO A COAGULANT SPIN BATH, WITHDRAWING THE RESULTING SWOLLEN WET SPUN CELLULOSE TRIESTER FILAMENTARY MATERIAL FROM SAID SPIN BATH, AND IMMERSING SAID SWOLLEN FILAMENTARY MATERIAL IN A SUBSEQUENT BATH CONTAINING A HYDROCARBON OIL HAVING AN ALIPHATIC CHAIN OF AT LEAST ABOUT 14 ATOMS AND HAVING A MOLECULAR WEIGHT OF AT LEAST ABOUT 200, A MELTING POINT BELOW ABOUT 50*C., A BOILING POINT OF AT LEAST ABOUT 200*C. AND BEING LESS THAN ABOUT 10% SOLUBLE IN SAID CELLULOSE TRIESTER, AND THEREAFTER DRYING SAID FILAMENTARY MATERIAL. 